The present invention relates to calibration rigs for calibration and/or re-calibration of flow meters and/or flow meter calibration carts.
Flow meters are commonly used devices for measuring a flow of a liquid through a pipe. In various branches of industry, for example in the chemical industry or in the pharmaceutical industry, the measurement data obtained by flow meters is used to control complex industrial processes. Exact measurements of the flow are very important. Therefore flow meters are carefully calibrated before they are first installed. Also regular re-calibration is performed in order to ensure high accuracy of measurements over long periods of time.
Flow meters are currently calibrated on flow meter calibration rigs comprising a large reservoir of treated city water. The water is circulated through the flow meter to be calibrated and then to a diverter. The diverter either diverts the water back to the reservoir or to a weigh tank. The weigh tank is used to determine a quantity of water it obtained from the flow meter and is then emptied into the reservoir. The water supply in the reservoir is reused on the rig many times. The water reservoir is completely emptied, cleaned and refilled typically only once a year.
Problems can occur, when used flow meters are re-calibrated in this way. Even if all flow meters have been cleaned and decontaminated before re-calibration, it can not be guaranteed that they are absolutely free of all hazardous contaminates. First of all it is very difficult to determine all contaminants the flow meter has been exposed to and secondly substances that are considered harmless by most users may very well be considered a dangerous contaminant in another industry. An example for this are proteins. Whereas most industries do not consider proteins to be contaminants, they can very well be contaminants in a biological or pharmaceutical process.
A potentially contaminated flow meter can thus contaminate the water. This contaminated water can then become a potential source of contamination of flow meters that are calibrated or re-calibrated on the rig later on.
The same problems occur when flow meter calibration carts are calibrated and/or re-calibrated. Flow meter calibration carts are mobile units designed for on site calibration or re-calibration of flow meters. They comprise a flow meter that is designed to perform a reference measurement of a flow on site. Data from this reference measurement is used for calibration and/or re-calibration of the flow meter on the site. During the process of calibration or re-calibration the flow meter calibration cart is either installed in a pipe leading up to the flow meter to be calibrated or re-calibrated or it is installed in parallel to the flow meter. In the first case the flow through the flow meter calibration cart and the flow through the flow meter are identical. In the second case the flow through the flow meter corresponds to the flow through the flow meter calibration cart multiplied by a constant. The value of the constant depends on the mechanical and geometrical features of the calibration or re-calibration set up.
The flow meter to be calibrated or re-calibrated can remain on its position during the entire calibration procedure.
The flow meter inside the mobile flow meter calibration cart needs to operate with a high accuracy and reliability. Therefore flow meter calibration carts have to be calibrated and regularly re-calibrated, using calibration rigs. Consequently flow meter calibration carts are exposed to the same risks of contamination as flow meters.
It is an object of the invention to provide a flow meter calibration rig, that can be used for calibration and/or re-calibration of flow meters and/or flow meter calibration carts.
To this end the invention comprises a calibration rig comprising:                a source of pure sterilized water or a source of a sterile conductive solution,        a piping manifold connected to the source,        at least one flow meter connected to the source via the piping manifold and/or        at least one flow meter calibration cart connected to the source via the piping manifold and        a drain pipe connected to each flow meter and to each flow meter calibration cart to guide liquids from the flow meters and/or the flow meter calibration carts to a drain.        
According to a refinement of the invention, a calibrated reference flow meter is installed in parallel or alternatively in series to a flow meter or a flow meter calibration cart to be calibrated or re-calibrated.
According to a refinement of the invention a device for measuring a quantity of liquid received from a flow meter or a flow meter calibration cart is installed between the flow meter or the flow meter calibration cart and the drain pipe. Preferably the device for measuring a quantity of liquid is a weigh tank.
According to another refinement of the invention a device for supplying a predetermined quantity of liquid is installed between the source and the flow meter or the flow meter calibration cart.
Further the invention comprises a method of calibration or re-calibration of a flow meter or a flow meter calibration cart, comprising the steps of                mounting the flow meter or the flow meter calibration cart on a flow meter calibration rig according to the invention,        sending a quantity of pure sterilized water through the flow meter or the flow meter calibration cart,        directing the water from the flow meter or the flow meter calibration cart to a drain.        
Further the invention comprises a method of calibration or re-calibration of a flow meter, comprising the steps of                mounting the flow meter on a flow meter calibration rig according to one of the previous claims comprising a source of pure sterilized water,        adding a quantity of a sterile conductive solution to the pure sterilized water thus obtaining a sterile conductive liquid,        sending this sterile conductive liquid through the flow meter, and        directing the sterile conductive liquid from the flow meter to a drain.        
One advantage of the calibration rig is that even if calibration or re-calibration of contaminated flow meters or flow meter calibration carts is performed a contamination of the rig cannot occur. Thus subsequently calibrated or re-calibrated devices cannot become contaminated.
Since the liquid is sterile and never resupplied to the rig a decontamination of flow meters or flow meter calibration carts is no longer necessary prior to re-calibration.
The invention and further advantages are explained in more detail using the figure of the drawing, in which one exemplary embodiment is shown.